Many types of printing systems include one or more printheads that have arrays of dot forming elements that are controlled to make marks of particular sizes, colors, or densities in particular locations on the print media in order to print the desired image. In some types of printing systems the array(s) of dot forming elements extends across the width of the page, and the image can be printed one line at a time. However, the cost of a printhead that includes a page-width array of marking elements is too high for some types of printing applications so a carriage printing architecture is used.
In a carriage printing system (whether for desktop printers, large area plotters, etc.) the printhead or printheads are mounted on a carriage that is moved past the recording medium in a carriage scan direction as the dot forming elements are actuated to make a swath of dots. At the end of the swath, the carriage is stopped, printing is temporarily halted and the recording medium is advanced. Then another swath is printed, typically as the carriage is moved in the opposite direction, so that the image is formed swath by swath. In a carriage printer, the dot forming element arrays are typically disposed along an array direction that is substantially parallel to the media advance direction, and substantially perpendicular to the carriage scan direction. The length of the dot forming element array determines the maximum swath height that can be used to print an image. The longer the array length is the faster the printing throughput, because fewer swaths are needed to print the image. However, a longer array length requires more dot forming elements on a longer printing device, which increases the cost of the printing device. Fast printing throughput can be especially important for black and white documents, such as text documents, so a long array length for black can be more important than a long array length for color arrays.
In an inkjet printhead, the dot forming elements include nozzles that are connected to a supply of ink. In a color printing system, arrays of nozzles for printing different color inks (such as cyan, magenta, yellow and black) are typically separated from each other along the carriage scan direction. Such nozzles can be provided on different printheads. However, it can be advantageous to have nozzle arrays for a plurality of different colors resident on a single printing device within a single printhead. Printing devices that are fabricated using typical manufacturing technologies, including those used in the semiconductor industry, have nozzles on a single device that can be made to be very uniform in characteristics and well aligned to one another. This is advantageous because print quality is improved if the resulting dots are well-aligned to one another, and the printer can operate more reliably if operating conditions (including voltage and pulsewidth for forming dots) can be selected such that they are optimal or nearly optimal for all of the dot forming elements. Having the nozzles for a plurality of colors on a single printhead die also provides a more compact and cost effective configuration.
For carriage printers that use bi-directional printing and eject dots of one color ink on top of dots of a different color ink, it is known that the resultant color depends upon the order of ink laydown. Printing yellow ink on top of cyan ink results in a different color than printing cyan ink on top of yellow ink for example. Typically, the color laydown order is not an issue if one of the two inks is black. U.S. Pat. Nos. 4,528,576; 6,315,387 and 6,616,267 disclose providing additional color nozzle arrays that are symmetrically ordered (for example as cyan, magenta, yellow, magenta and cyan) so that whether printing left to right or right to left it is always possible to have the same color laydown order. In these patents, the different color arrays are separated from each other but in line with each other along the carriage scan direction. In other words, there is no nozzle array direction offset between different cyan, magenta and yellow arrays.
Many carriage printing systems include multipass print modes in which the dots in a given region of the recording medium are formed in a plurality of printing passes. In multipass printing, responsibility for printing each raster line of the image is shared between a plurality of dot forming elements. In this way the nonuniform marking behavior of dot forming elements can be disguised in order to provide improved image quality. For an inkjet printer, multipass printing can provide time for improving the uniformity of ink-media interactions by controlling the pattern of dots that can be printed within one pass, thereby reducing coalescence (i.e. flowing together of ink drops on the surface of the page before they soak into the page). Multipass printing can also enable multitone printing in which multiple dots are printed in the same pixel locations.
Printhead die are typically formed on wafers containing many die that are singulated by dicing, for example, after wafer fabrication. Die cost is roughly proportional to die area. However, wafer cost can also be influenced by the number of wafers of the same type that are produced. Wafers made in high volume are less costly than wafers made in low volume.
Consequently, a need exists for a nozzle array configuration for a printhead die that facilitates faster printing for black, provides excellent nozzle uniformity and alignment, and which can be separated from the wafer in different die sizes so that depending on the details of die singulation, different trade-offs can be provided for die cost and printing throughput, thereby enabling higher wafer fabrication volumes. It is further advantageous if at least one of the resulting printhead die types can address the problems of color laydown order to further improve image quality and printing throughput.